This invention is related to electromagnetic pumps and more particularly to electromagnetic flow couplers.
As is well known in the art, electromagnetic pumps produce a pressure differential or a pressure head between the inlet and the outlet through the interaction of an electrical current and a crossed magnetic field. This interaction produces an electromagnetic force density throughout the volume of the fluid within the pump region wherever both the current density and the magnetic field are non-zero. At each such point, this force is proportional not only to the magnitude of the current density and magnetic field, but also to their relative orientation. The maximum force density and resulting pressure differential occurs when the electrical current and the magnetic field are mutually perpendicular to each other and to the direction of fluid flow.
Typically, the electromagnetic pumps are constructed in a rectangular duct by mounting two electrodes flush with the opposite side walls of the duct and placing the other two walls between magnetic pole faces. When the two electrodes are connected to an external power supply, current flows across the duct and interacts with the magnetic field to produce the axially directed body force and pressure difference across the duct. The pump's inlet and exit regions are defined roughly by the electrode edges. These regions may vary somewhat depending upon the relative location of the magnetic pole face edges. In an ideal pump, all the current would be confined to the duct volume enclosed by the electrodes and the pole faces where the force density is the greatest. In an actual pump, however, some current leaks into the magnetic fringe region both upstream and downstream from the electrode edges. This tends to lower pump efficiency. Thus, current leakage in the magnetic fringe regions adds little to the overall pressure differential while increasing the current flow thereby diminishing efficiency.
In general, the problems with electromagnetic pumps fall into two categories: (1) obtaining suitable high current power supplies, and (2) minimizing parasitic losses in the containment walls of the pump. Parasitic losses in the containment duct walls of electromagnetic pumps account for much of its low efficiency which may be in the range of 10 to 40%. To overcome the problems of obtaining a suitable high current power supply and to minimize parasitic losses, two electromagnetic pumps may be arranged side-by-side in a common magnetic field with one such pump acting as an electromagnetic generator and the other acting as an electromagnetic pump. This arrangement of electromagnetic pumps is commonly referred to as a "flow coupler".
In a typical flow coupler, a liquid metal is caused to flow through the generator section of the flow coupler. Passage of the fluid through the common magnetic field generates a large current which is transferred to the pump section by short, low resistance electrodes. Interaction of the current in the pump section with the common magnetic field produces flow in the pump section. In this manner, the flow of a first liquid metal in the generator section is "coupled" to the flow of a second liquid metal in the pump section. The local generation of the current enables lower voltages and higher currents to be used than would be possible with an external power supply. The lower voltages, in turn, reduce end current losses and permit higher overall efficiencies, on the order of 60%, to be attained.
While flow couplers are capable of increasing electromagnetic pump efficiencies, further reduction of parasitic containment wall losses would be desirable. Therefore, what is needed is an electromagnetic flow coupler constructed to minimize parasitic current losses in the duct walls of the flow coupler.